Set of symbols
Deduction system
Zermelo-Fraenkel set theory
Transitive set
Ordinal number
Cardinal number
Set cardinality
Singleton set
Set of singletons
Singleton map
Formulation 0
Let $X$ and $Y$ each be a D11: Set such that
(i) \begin{equation} \{ \{ x \} : x \in X \} \subseteq Y \end{equation}
The singleton map from $X$ to $Y$ is the D18: Map \begin{equation} X \to Y, \quad x \mapsto \{ x \} \end{equation}
Child definitions
» D4493: Canonical singleton map